Foaming a hard case - suggestions?

[Philip Jensen]

OK, here's the deal. This weekend, I've bartered my way into foaming-in an empty fiberglass case to fit a friend's tuba. This will be for flight purposes. I haven't seen the case yet, but I'm told it is quite light but very strong.

I'm currently planing on foaming just the main body area and not the bell. I'm also contemplating having the bottom bow float in air too.

I was thinking about making a custom fit plug for the bell too

Here is my current strategy.


Cover tuba and line case with sheets of plastic.

I'm thinking about wrapping some fabric around the horn before the plastic to compensate for the thickness of material that will be glued to the foam afterwards.

I was also planning to place something (cheap tuperware?) over the tops and bottoms of the valves (piston)

Start with 3 dollops of foam in the bottom of the case and position horn as desired. Brace as needed. Let foam set.

Once set, fill in remaing bottom half of case, leaving bell area unfoamed. I'll probably let the foam come up over the sides a bit

Should I leave the bottom bow area unfoamed too?

I was thinking about including a strap that would go against the wall of the case so the horn could be strapped in place against the foam.

I assume I'll have to cut the tuba out of its plastic wrap as that will be stuck to the foam.

Once the bottom is set, place 3 dollops on top of the horn and close case, let cure. This will set the thickness for the top half.

Open case, put tuba in top half of the case and fill with more foam

Once all cured, remove horn and trim sides so case closes properly

If I hate it, since I lined the case with plastic, I can take it out and try again.

Assuming it is great, I still will take the foam out, spray it with a lot of spray adhesive and cover the tops and sides with appropriate fabric and then probably use construction adhesive to caulk the fabric covered foam into the case

Regular Stuff or the super expanding Stuff?

Anything I've left out?

I need to ask if they want an area set aside for music, mouthpieces, etc. I guess that may depend on how much room there is is the case.

Thanks in advance for any suggestions

I may photo document the process if anybody is interested.

[MaryAnn]

I would love to see photographs of this.

Based on having used expanding foam to fill in a large doggie door in the wall of my house....I'd say be careful with it. Because it will ooze out all over everything, due to your inability to guess how much to put in in the first place. I would use the non-expanding and just keep filling in the gaps.

Of course I love the idea of not foaming the bell; you probably have read my opinions of doing that. The bottom bow....reminds me of what my private Kung Fu teacher taught me about getting hit in the ribs: if you hunch over so your ribs are closer together, when someone whacks you there is more to take up the blow and you're a lot less likely to get a cracked rib. So if you foam the bottom bow so there isn't single-point stress when the case is dropped, it should work fine.

the tupperware is a good idea too.

I would want my design to have support for the heaviest part of the tuba no matter what angle the case was dropped at, so it couldn't slam around inside.

My only concern about foam is if it ends up rock hard and has no resiliency. I'd want it to have some.

Your idea of leaving room for the fabric is good.

I hope this works out and becomes the industry standard.

MA

[Rick Denney]

Remember that the point of the material in the case is to control G forces, and to make sure they are transmitted to the instrument at places where the instrument can take the load.

That's the reason for leaving the bell in open air. The only way you can load the bell is edge-on. Any other loading will curl the edge.

If you use stiff foam, it will transmit more G forces to the instrument that soft foam. But if it fits tightly over enough area, the load will be distributed widely enough to prevent failure. Thus, I think I'd go ahead and foam in the bottom bow, which is pretty strong and has a lot of useful surface area.

The advantage to setting foam you propose is that when it crushes, it does not expand back out, and it therefore absorbs G forces rather than delivering them back to the instrument. That also means that if you find it has been crushed for any reason, you may need to do it all again. Of course, it also means your tuba was protected.

Don't use expanding foam. It could even crush the instrument while it is expanding. Even the non-expanding stuff expands considerably, so build in layers.

There is also latex foam out there that is water-soluble when wet. This would be lots easier to clean up if it gets out of hand. It's also not as stiff as the polyurethane foam, but it may also not be as strong.

The air space around the bell needs to be big enough to allow the instrument to move freely under all possible conditions. With stiff foam, that may not require that much air.

You definitely need a cavity around the valve mechanisms.

After putting the tupperware box over the valves, I would consider wrapping the tuba in a stretchy knit fabric, then in a plastic garbage bag. Then hook up the bag to a shop vac and suck all the air out so that the bag is drawn down to the instrument tightly. Wrinkles don't matter. Seal the bag, and then start your foaming process.

I would also consider locating the instrument with a few blocks of soft foam rubber at a couple of spots where you'd like not to apply too much force in use. You could even jam foam rubber around the bell to hold that end of the instrument, and then remove it later after the foaming process. It would hold the instrument in position and let you foam from the inner-most recesses first. Lay the instrument in one side of the case, foam that side up to three inches below the edge, let the foam cure, and the add foam to the close to the edge. When that has cured, remove the instrument and cut the foam flush with the edge of that half of the case with a serrated knife, using a sawing motion. Then do the other half the same way. You may have to replace the garbage bag because as you way you'll have to cut it because it will have stuck to the foam.

Make sure you have a way to keep the instrument from sliding out of the foam in the direction of the bell opening. Either provide a good coverage of foam over the upper bow (that would work on, say, a Miraphone 186 CC that has a low top bow), or provide a wide strap that restrains the body of the instrument in that direction. Another way to accomplish the same thing is by making a plug for the bell that fits on the inside of the bell and holds the edge of the bell away from the end of the case. Charlie Krause has suggested using a partly-inflated soccerball as a plug, and I think this is a good idea. It loads the bell in ways that make use of its strength.

Rick "who has gone this thought process before, but who doesn't need a flight case and has therefore not experimented" Denney

[Dan Schultz]

I used to use a product called 'Instapak' for packing dental equipment. It is very good stuff but you have to know how much to use to fill the space. I would not attempt to pack a tuba in this stuff unless I have some experience behind me. As far as the expanding foam crushing the tuba.... it probably won't... but if you confine the foam and don't allow it to expand to the prescribed pounds per cubic foot you will get a higher density foam, which defeats the purpose.

Build a permanent foam shipping container for your tuba out of laminations of 2" foam rubber glued together.

[Rick Denney]

I used to use a product called 'Instapak' for packing dental equipment. It is very good stuff but you have to know how much to use to fill the space. I would not attempt to pack a tuba in this stuff unless I have some experience behind me. As far as the expanding foam crushing the tuba.... it probably won't... but if you confine the foam and don't allow it to expand to the prescribed pounds per cubic foot you will get a higher density foam, which defeats the purpose.

Build a permanent foam shipping container for your tuba out of laminations of 2" foam rubber glued together.

I used that Great Stuff foam to seal a door on the front of my house in Dallas, and it expanded enough to bow the door jamb so that the door wouldn't close. And that was with screws every 18 inches. That's why I offered my warning.

I agree with you that it is probably better to build up the foam from sheet foam of the appropriate density in laminations, using 3M #77 foam adhesive. But one thing I like about the spray foam is that it is not elastic--when it crushes, it stays crushed and doesn't deliver the force back to the tuba. Does that matter? Probably not, if the foam used has a tight texture and enough polybutylene to provide damping. A little of that "swedish mattress" stuff might be a good thing there.

Good foam can be bought at an upholstery supply house, but bring your wallet--it's expensive.

Rick "who has made several cases using foam rubber" Denney

[Chuck(G)]

You may also want to think about visiting a marine supply store--the nuatical trade fills bulkheads with expanding foam, so it's available in larger quantities.

Be careful with any expanding foam--some folks are very allergic to the stuff. Wear a mask and eye protection.

[cambrook]

As Rick pointed out the expanding foam has a lot of strength. It can also behave very differently depending on the amount that is used at any time. The amount of heat generated and expansion is not linear - twice the foam is more than twice the heat etc

I wouldn't be rushing to do this with my tuba, I would at least block out as much as possible of the free space in the case with polystyrene foam first, and maybe use the expanding foam to fill in just the small areas left.

Good luck!

[Dan Schultz]

I used to use a product called 'Instapak' for packing dental equipment. It is very good stuff but you have to know how much to use to fill the space. ......
Build a permanent foam shipping container for your tuba out of laminations of 2" foam rubber glued together.

I used that Great Stuff foam to seal a door on the front of my house in Dallas, and it expanded enough to bow the door jamb so that the door wouldn't close. And that was with screws every 18 inches. That's why I offered my warning...... Good foam can be bought at an upholstery supply house, but bring your wallet--it's expensive.

Rick "who has made several cases using foam rubber" Denney

You are soooo right! I wouldn't even attempt to use a product like 'Great Stuff' to make the foam inserts. It's not the same 'stuff' as 'Instapak' and is designed only to be caulking sealant (expanding or non-expanding).... NOT a packing material. When 'Great Stuff' ages, it is very stiff and will not absorb shock very well.... especially over a large area. Even if you support a tuba fully, it won't stop the opposite side of the horn from trying to catch the other if the G forces are high enough.

[Art Hovey]

I tried using foam in a spray can to make a bell plug for my tuba, and you may wish to learn from my mistakes:
First I cut out sheets from plastic garbage bags and stuck them onto the inner surface of the bell with scotch tape. Then I cut a styrofoam disk to fit about a foot down into the bell. I ran a wooden rod through that disk to provide a handle for pulling out the plug, and fastened it to a piece of plywood under the disk.
Then I set the tuba upright and filled the bell with spray foam from Home Depot.
What I learned was that the stuff does not harden if it is more than two or three inches thick. The top surface hardened, but the inner part that was not exposed to the air remained gooey for 24 hours, expanding and flowing betwen the plastic sheets and the tuba bell. If there had been lacquer on that tuba it would have been ruined.
The moral of the story is that you can't expect the project to work right on the first try. Do some experimenting and testing first. And please do post some picture and tell us how your project turns out.